Calibration assembly for aide in detection of analytes with electromagnetic read-write heads

ABSTRACT

According to one embodiment, a calibration assembly includes an outer layer having at least one calibration trench extending along a y-axis, and an encapsulation layer within the calibration trench. The encapsulation layer has a plurality of nanoparticles spaced apart along said y-axis of said at least one calibration trench. Each of said plurality of nanoparticles are provided at known y-axis locations in said calibration trench, and each of the plurality of nanoparticles have a known magnetic property.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/099,358, filed May 3, 2011, and which is herein incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to devices and processes that incorporateelectromagnetic write-heads and magneto-resistive read sensors to detectmagnetized nanoparticles.

BACKGROUND OF THE INVENTION

It is known that antibodies bind with antigens as part of the humandisease defense system. Presently, antigens are detected by suchtechniques as immunofluorescence, immunoperoxidase, or enzyme-linkedimmunosorbent assay (ELISA), each of which then employs a microscope forvisual detection of the target antigen. It is desirable to exploit theuse of magnetic signaling technology to automate the detection ofanalytes, such as antigens, and to further apply this technology to thedetection of any biological matter. Still further, it is important toensure that the equipment utilized is reliable and accurate in thedetection of analytes.

SUMMARY OF THE INVENTION

Electromagnetic read heads are useful in detecting analytes viananoparticle-labeled substances. However, is important to ensure thatthe equipment utilized to detect the antigens is reliable and accurate.Accordingly, one embodiment of the invention includes a calibrationassembly which has nanoparticles with known magnetic properties, thenanoparticles spaced apart at known y-axis locations along thecalibration assembly.

For example, an embodiment of forming a calibration assembly includesforming at least one calibration trench within an outer layer. Thecalibration trench extends along a y-axis. An encapsulation layer isformed within the calibration trench and a plurality of nanoparticlesspaced apart along the y-axis are provided in the encapsulation layer.Each of the plurality of nanoparticles are provided at known y-axislocations in the calibration trench. Further, each of the plurality ofnanoparticles have a known magnetic property. The encapsulation is curedsuch that the plurality of nanoparticles are encapsulated within theencapsulation layer at the known y-axis locations.

The calibration assembly may be used to calibrate a matched filter ofthe write and read circuitry. Because the calibration assembly comprisesnanoparticles with known magnetic properties the read response of theread circuitry to a particular nanoparticle may be stored in the matchedfilter as an ideal signal for that nanoparticle. The ideal signal storedin the matched filter may then be utilized for reliably and accuratelydetecting antigens. Still further, the ideal signal stored within thematched filter of the write and read circuitry may be utilized in amanufacturer's or user's correlation test of a calibration assembly toensure that the calibration assembly is within the manufacturer's oruser's acceptable standards for calibration of their write and readassemblies.

For a fuller understanding of the present invention, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a calibration assembly, not to scale, inaccordance with an embodiment of the invention;

FIG. 2A is a cross-sectional view of a portion of a calibrationassembly, not to scale, including a calibration trench in accordancewith an embodiment of the invention;

FIG. 2B is a cross-sectional view of a portion of a calibrationassembly, not to scale, including a calibration trench in accordancewith an embodiment of the invention;

FIG. 2C is a cross-sectional view of calibration assembly, not to scale,including calibration trenches and an alignment trench in accordancewith an embodiment of the invention;

FIG. 3A illustrates a plan view of the calibration assembly, not toscale, having nanoparticles placed at known y-axis locations inaccordance with an embodiment of the invention;

FIG. 3B is a cross-sectional view of the calibration assembly, not toscale, having nanoparticles in accordance with an embodiment of theinvention;

FIG. 3C is a graphical representation of the calibration assembly, notto scale, having nanoparticles at known y-axis locations in accordancewith an embodiment of the invention;

FIG. 4 is a flow chart illustrating the steps of preparing thecalibration assembly in accordance with an embodiment of the invention;

FIG. 5 illustrates control circuitry for the x-axis and y-axis motion ofthe head-module in an embodiment of the invention;

FIG. 6 illustrates read and write circuitry in an embodiment of theinvention;

FIG. 7 is a flow chart illustrating the process of calculating animpulse response of an ideal signal profile of a detected nanoparticlein accordance with an embodiment of the invention;

FIG. 8A illustrates the detection signal profile read by read sensorwhen a nanoparticle is detected in accordance with an embodiment of theinvention;

FIG. 8B illustrates the impulse response of an ideal signal profile ofthe detected nanoparticle in accordance with an embodiment of theinvention;

FIG. 8C illustrates the calculated correlation for the detection signalprofile of each nanoparticle detected by read sensor in accordance withan embodiment of the invention;

FIG. 9A illustrates the detection signal read by read sensor whenmultiple nanoparticles are detected in accordance with an embodiment ofthe invention;

FIG. 9B illustrates the impulse response of the ideal signal profiles ofmultiple detected nanoparticles in accordance with an embodiment of theinvention;

FIG. 9C illustrates the calculated correlation for the detected signalprofiles of multiple detected nanoparticles by read sensor in accordancewith an embodiment of the invention;

FIG. 10A is a flow chart illustrating the process of performing acalibration correlation test for a calibration assembly 100 inaccordance with an embodiment of the invention;

FIG. 10B is a flow chart illustrating further details of performing thecorrelation test on the calibration assembly in accordance with anembodiment of the invention;

FIG. 11 is a schematic diagram of a current-in-plane (CIP) read-sensorwhich may be used in conjunction with various embodiments of theinvention;

FIG. 12A shows a schematic diagram of the current flow through a GMRstack and the associated magnetic fields as viewed along a slice in thestack when a forward (positive) bias current is applied in accordancewith an embodiment of the invention;

FIG. 12B is a schematic diagram of the current flow through a GMR stackand the associated magnetic fields as viewed along a slice in the stackwhen a reverse (negative) bias current is applied in accordance with anembodiment of the invention;

FIG. 12C is a schematic diagram of the net magnetization inside the freelayer of a generic GMR stack; and

FIG. 13 illustrates a process of calibrating a read sensor of the headmodule in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in exemplary embodiments in thefollowing description with reference to the Figures, in which likenumbers represent the same or similar elements. While the invention isdescribed in terms of the best mode for achieving the invention'sobjectives, it will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

In copending and coassigned U.S. patent application Ser. No. 12/888,388entitled “DETECTION OF ANALYTES VIA NANOPARTICLE-LABELED SUBSTANCES WITHELECTROMAGNETIC READ-WRITE HEADS”, and Ser. No. 12/970,837 entitled“TRENCHED SAMPLE ASSEMBLY FOR DETECTION OF ANALYTES WITH ELECTROMAGNETICREAD-WRITE HEADS,” a sample assembly and method of detecting antigens isdescribed utilizing electromagnetic read heads and are herebyincorporated by reference.

It is important to ensure that the equipment utilized to detect antigensis reliable and accurate. Accordingly, one embodiment of the inventionincludes a calibration assembly having nanoparticles, with knownmagnetic properties, spaced apart at known y-axis locations along thecalibration assembly. In one embodiment, the calibration assembly may beused to calibrate a matched filter of the write and read circuitry.Because the calibration assembly comprises nanoparticles with knownmagnetic properties the read response of the read circuitry to aparticular nanoparticle may be stored in the matched filter as an idealsignal for that nanoparticle. The ideal signal stored in the matchedfilter may then be utilized for reliably and accurately detectingantigens. Still further, the ideal signal stored within the matchedfilter of the write and read circuitry may be utilized in amanufacturer's or user's correlation test of a calibration assembly toensure that the calibration assembly is within the manufacturer's oruser's acceptable standards for calibration of their write and readassemblies.

Magnetic sensors, such as GMR sensors, contain magnetic materials whosecombined effect is to have a resistance change when subjected to amagnetic field. When subjected to low-level electrical overstress (EOS)or electrostatic discharge (ESD) current/voltage pulses the GMR sensorscan be damaged or degraded. Still further, corrosion can damage magneticsensors over time, reducing the signal strength and possibly leading tofailure. In one embodiment, a method of determining if a read sensor isdamaged or degraded is described. Still further, if it is determinedthat a read sensor is degraded, a method of calibrating a read sensor isdescribed. Calibration of each individual read sensor allows for uniformread responses from each of the read sensors on a read head, andprevents unreliable an inaccurate detection of analytes due to sensordegradation.

FIG. 1 is a top view of a calibration assembly 100, not to scale, inaccordance an embodiment of the invention. The calibration assembly 100includes a substrate 199. The substrate 199 may comprise, withoutlimitations, a Peltier hard-substrate, a glass substrate, a polyethyleneterephthalate (PET, which is commonly known by the trade name of Mylar™)substrate, a flexible-substrate, or other materials having similarproperties. The term “substrate” refers to any supporting structure,including, but not limited to, the substrates described above. Further,the substrate may include of more than one layer of material.

As shown in FIGS. 2A, 2B, and 2C, an outer layer 253 is formed oversubstrate 199. Deposition techniques utilized herein include, but arenot limited to, photolithography, silk-screening, and other similarprocesses. The outer layer may comprise diamond-like-carbon,polytetrafluoroethylene, aluminum oxide, polyamides, or otherlow-friction materials known in the art. The outer layer 253 may beformed to a thickness of between 0.2 to 60 microns. The outer layer 253includes calibration trenches 180. The process of forming thecalibration trenches 180 is described with respect to FIGS. 2A and 2B.

One embodiment of forming calibration trenches 180 is illustrated inFIG. 2A. In this embodiment, a base layer 252 is formed on substrate199. Base layer 252 may comprise nonmagnetic materials such as gold,silicon, or SiO₂, or other materials having similar magnetic properties,without limitation. An outer layer 253 is then formed on base layer 252.Outer layer 253 has an upper surface 254. A plurality of calibrationtrenches 180 are formed within outer layer 253. Calibration trenches 180may be formed by known methods in the art including laser milling, x-raymilling, or photolithographically. Calibration trenches 180 may beformed to have a depth of between 0.2 to 60 microns. It should beunderstood by one of ordinary skill in the art that, while only onecalibration trench is shown, a plurality of calibration trenches 180 maybe formed within the outer layer 253 with the same method describedherein. Each calibration trench 180 is formed having a bottom surface255. In one embodiment, the bottom surface of the trench exposes baselayer 252.

Another embodiment of forming calibration trenches 180 is described withrespect to FIG. 2B. In this embodiment, outer layer 253 is formed onsubstrate 199. The outer layer 253 has an upper surface 254. A pluralityof calibration trenches 180 are formed within outer layer 253.Calibration trenches 180 may be formed by known methods in the artincluding laser milling, x-ray milling, or photolithographically.Calibration trenches may be formed to have a depth of between 0.2 to 60microns. It should be understood by one of ordinary skill in the artthat, while only one calibration trench is shown, a plurality ofcalibration trenches 180 may be formed within the outer layer 253 withthe same methods described herein. Each calibration trench 180 is formedhaving a bottom surface 255. Base layer 252 is formed within eachcalibration trench 180 and on the bottom surface 255 of each calibrationtrench 180. Base layer 252 may comprise nonmagnetic materials such asgold, silicon, or SiO₂, or other materials having similar magneticproperties, without limitations. As shown in FIG. 2B, the base layer 252only partially fills calibration trenches 180. There are manyembodiments in which base layer 252 may be formed to only partially fillcalibration trenches 180. For example, in one embodiment, base layer 252may be formed conformally over the outer layer 253 and withincalibration trenches 180. Base layer may then be removed by etching orplanarization techniques known in the art. Alternatively, the base layer252 may be selectively deposited by known methods in the art. Thedescribed embodiment of forming a base layer 252 only within thecalibration trench 180 is particularly advantageous in embodiments inwhich expensive materials are utilized, such as gold since much lessmaterial is required to form the base layer 252.

It is important to note that the base layer 252 may be omitted whenforming the calibration assembly 100. However, the base layer may beformed on the substrate 199 in order for the calibration assembly 100 tobe similar to that of a sample assembly as described in copending andcoassigned U.S. patent application Ser. No. 12/970,837 entitled“TRENCHED SAMPLE ASSEMBLY FOR DETECTION OF ANALYTES WITH ELECTROMAGNETICREAD-WRITE HEADS.”

For example, as shown in FIG. 1, eight calibration trenches 180 may beformed to correspond to the head-module 104 of the IBM® TS 1130 writingwith eight write elements 106 and reading with eight read sensors 108simultaneously, as further explained below. The calibration trenches 180are parallel to each other and extend in along the y-axis.

In one embodiment, as shown in FIGS. 1 and 2C, the outer layer 253further includes at least one servo alignment track 194 with a pluralityof magnetic servo alignment marks 193. The servo alignment track 194 isparallel with the calibration trenches 180 and extends along the y-axis.The servo alignment track 194 may be a servo alignment trench 194 with aplurality of magnetic servo alignment marks 193. FIG. 2C shows a crosssection of substrate 199 along the x-axis illustrating an embodiment inwhich an alignment trench 194 is formed within outer layer 253. Forsimplicity of illustration, base layer 252 is not illustrated in FIG.2C. Alignment trench 194 may be formed in the same manner as describedfor forming calibration trenches 180 shown in FIGS. 2A and 2B. In oneembodiment, alignment trench 194 is formed simultaneously with theformation of calibration trenches 180. Specifically, alignment trench194 may be formed by known methods in the art including laser milling,x-ray milling, or photolithographically. Alignment trench 194 may have adepth of between 0.2 to 60 microns. It should be understood by one ofordinary skill in the art that, while only one alignment trench 194 isshown, a plurality of alignment trenches 194 may be formed within theouter layer 253 as described herein. For example, alignment trenches 194could be formed between each of the calibration trenches 180.

In this embodiment, calibration trenches 180 may be masked and the servoalignment trench 194 is filled with tape ink. The tape ink, whichcontains magnetic recording particles in a polymer matrix, is cured bymethods known in the art. Magnetic encoded servo alignment marks 193 aresubsequently encoded in the cured tape ink.

In another embodiment, magnetic encoded servo alignment marks 193 areencoded on a piece of magnetic tape which is adhered to outer layer 253.Further, the magnetic encoded servo alignment marks 193 may be encodedby the manufacturer of substrate 199 on the magnetic tape. Magneticencoded servo alignment marks 193 may be in the form of timing basedservo marks as taught by U.S. Pat. No. 7,639,448 entitled “DifferentialTiming Based Servo Pattern for Magnetic-Based Storage Media,” which ishereby incorporated by reference in its entirety. Servo alignment marks193 are read by read sensor 108 and used to keep the write elements 106and read sensors 108 in alignment with calibration trenches 180 alongthe x-axis while the head module 104 moves relative to calibrationtrenches 180 along the y-axis.

Still further, in one embodiment the alignment marks 193 may benon-magnetic marks. For example, the alignment marks may belithographed, silk-screened or ink-jet printed, and read with an opticallaser.

The preparation of the calibration assembly 100, including the formationof the nanoparticles within the calibration trench 180 is discussedfurther with respect to FIGS. 3A, 3B, 3C and 4. FIG. 3A illustrates planview of calibration assembly 100 having nanoparticles 212A, 212B, and212C placed at known y-axis locations. FIG. 3B is a cross-sectional viewof the calibration assembly 100 having nanoparticles 212A, 212B and212C. FIG. 3C is a graphical representation of the calibration assembly100 having nanoparticles at known y-axis locations. FIG. 4 illustratesthe steps of preparing the calibration assembly 100. For simplicity ofexplanation, FIGS. 3A, 3B and 3C show only a single calibration trench180 and an embodiment in which the base layer 252 is formed within thecalibration trench 180. However, it should be understood that thecalibration assembly 100 may have a plurality of calibration trenches180 and the base layer may be formed by any of the methods describedherein. Similarly, although FIGS. 3A, 3B, and 3C show only threenanoparticles 212, one of ordinary skill in the art would understandthat any number of nanoparticles 212 may be provided.

As discussed above, an outer layer 253 is formed on substrate 199. Instep 402, at least one calibration trench 180 is formed in outer layer253. Base layer 252 is formed on the bottom surface 255 of thecalibration trench 180.

In step 404, an encapsulation layer 258 is formed within the calibrationtrench 180. The encapsulation layer 258 may comprise a polymer resinincluding epoxies, acrylates, cyanoacrylates and silicones. Theencapsulation layer 258 may include the addition of a thermalpolymerization initiator such as azobisiobutyronitrile, or a UVpolymerization initiator such as benzoylperoxide.

In step 406, nanoparticles 212A, 212B and 212C are provided at knownspaced apart y-axis locations within the calibration trench 180. Forexample, as shown in FIG. 3C, nanoparticle 212A is located at the y-axislocation of calibration trench 180 at y₁. Further, nanoparticle 212B islocated at the y-axis location of calibration trench 180 at y₂. Stillfurther, nanoparticle 212C is located at the y-axis location ofcalibration trench 180 at y₃. As shown in FIG. 3B, the nanoparticles212A, 212B and 212C (which may hereinafter be referred to as 212)include a magnetic inner core 216A, 216B, and 216C (which mayhereinafter be referred to as 216) and an outer shell 214A, 214B, and214C (which may hereinafter be referred to as 214). Magnetic inner cores216 may comprise hard magnetic materials with high coercivity, such asFe₂O₃, CrO₂, and Barium Ferrite BaFe. For example, magnetic inner cores216 may comprise iron oxide based nanoparticle materials, including MFe₂O₄ (where M may be Co, Ni, Cu, Zn, Cr, Ti, Ba, or Mg) nanomaterials,and iron oxide coated nanoparticle materials or other structures withsimilar functionality. The inner cores 216 are coated with anouter-shell 214 of nonmagnetic gold, silicon, or SiO₂, to createnanoparticles 212.

In one embodiment, the nanoparticles 212A, 212B, and 212C are the samenanoparticle (e.g. the same inner core 216 with the same outer shell214) such that the nanoparticles 212A, 212B, and 212C have the samemagnetic properties. In other embodiments, at least one of nanoparticles212A, 212B, and 212C may be different than the other nanoparticles 212A.212B, and 212C (e.g. may have at least one of a different inner core 216and a different outer shell 214) such that the at least one nanoparticle212A, 212B, and 212C has different magnetic properties than the othernanoparticles 212A, 212B, and 212C. In either embodiment, the magneticproperties of each nanoparticle 212A, 212B, and 212C at each y-axislocation is known.

It is important to note that magnetized nanoparticles are prone toagglomerate and form lumps. Therefore, in one embodiment, the magneticinner cores 216 of nanoparticles 212 are demagnetized. For example, inone embodiment, the magnetic inner cores 216 of nanoparticles 212 areheated above their Curie temperature to demagnetize the inner cores 216.The heated magnetic inner cores 216 are allowed to cool. Theaforementioned demagnetization step keeps the inner cores 216 ofnanoparticles 212 as individual particles.

In another embodiment, the step of demagnetizing the inner cores 216 ofnanoparticles may be omitted. The process of manufacturing the innercores 216 of nanoparticles may include a step of high temperaturesintering. Thus, the manufacturing process of the nanoparticles 212 maydemagnetize the inner cores 216. The formation of nanoparticles istaught without limitation by U.S. Pat. No. 6,962,685, entitled“Synthesis of Magnetite Nanoparticles and the Process of Forming,” whichis hereby incorporated by reference in its entirety.

In step 408 the encapsulation layer 258 is cured. As described above,the encapsulation layer 258 may include the addition of a thermalpolymerization initiator such as azobisiobutyronitrile, or a UVpolymerization initiator such as benzoylperoxide. Accordingly, a thermalcuring treatment or UV exposure curing treatment may be performed oncalibration assembly 100 such that the encapsulation layer 258 hardensand encapsulates the nanoparticles 212A, 212B, and 212C at theirrespective known y₁, y₂, and y₃ locations

Returning to FIG. 1, head module 104 includes electromagneticwrite-heads 106 and magneto-resistive read sensors 108 arranged inpairs, such that each write head 106 is paired with a read sensor 108.The write head 106 may be a thin film write element. The electromagneticwrite-heads 106 first write to calibration trenches 180, and then theadjacent magneto-resistive read sensors 108 immediately reads fromcalibration trenches 180, which is referred to as a read-after-writeoperation. In an exemplary embodiment of the invention, the calibrationassembly 100 has eight calibration trenches 180 corresponding to eightbits in a byte. Accordingly, in this embodiment, the head moduleincludes eight electromagnetic write-head 106 and magnetoresistive readsensor 108 pairs. Advantageously, this is the same number of write headsand read sensors in a typical head-module used in magnetic tape driveproducts, such as IBM® TS 1130. Therefore, in one embodiment the headmodule 104 may be an IBM® TS 1130 head module. It should be understood,however, any number of calibration trenches 180 may be used, and thenumber of electromagnetic write-head 106 and magneto-resistive readsensor 108 pairs in head-module 104 may be any number. The number may bein the range from one to the number of electromagnetic write-head andmagneto-resistive read sensor pairs the head-module 104. For example, inan embodiment in which there are sixteen such electromagnetic write-headand magneto-resistive read sensor pairs, such as in a head module of anIBM® 3480 tape drive, the number of calibration trenches may be sixteen.In one embodiment, the number of calibration trenches 180 is an integralmultiple of the number of write-head 106 and read sensor 108 pairs.Still further, in one embodiment, the write-head 106 and the read sensorare not separate devices. Instead a single head may perform thefunctions of both the write-head 106 and read sensor 108.

As mentioned above, the calibration trenches 180 may have spacing fromone calibration trench to the adjacent calibration trench along thex-axis to match the spacing from one read sensor 108 to the adjacentread sensor 108 along the x-axis. In one embodiment the spacing betweenone calibration trench 180 and an adjacent calibration trench 180 is166.5 microns to match the read sensor to read sensor spacing of theTS1130 tape drive.

Write-heads 106 may be any write head known in the art. In oneembodiment write-heads 106 comprise miniature electromagnets, with acoil sandwiched between two poles. Read sensors 108 may be anisotropicmagneto-resistive (AMR), giant magneto-resistive (GMR), or tunnelmagneto-resistive (TMR) read sensors, or other devices with similarfunctionality known in the art. AMR sensors are made from magneticalloys with intrinsic magnetoresistive (MR) behaviors. GMR read sensors,which are also known as spin-valve read sensors have synthetic MRproperties composed of multi-layered magnetic and non-magneticmaterials. A GMR sensor typically has a conductive metal (often Cu)sandwiched between a ferromagnetic pinned layer (PL2) and a softmagnetic free layer (FL). The GMR effect arises from electronsscattering off the PL2 and FL such that the scattering depends on thecosine of the angle between the magnetic moments in PL2 and FL.Typically, a GMR has an additional ferromagnetic pinned layer (PL1)which is magnetized anti-parallel, to PL1. There are several reasons forusing anti-parallel PL1 and PL2 rather than a single PL2.

To achieve a high GMR effect requires a thicker PL2. In order to tunethe GMR sensor, though, it is desired to have a low net moment impingingon the FL. To do so, would require a thin PL2, which is both difficultto control in a process, is less stable, and has a lower GMR ratio thana thick PL2. The above mentioned criteria can be satisfied by making PL2and PL1 anti-ferromagnetically coupled ferromagnets. Furthermore, sincePL1 and PL2 have a very strong antiferromagnetic coupling, they arehighly stable. TMR read sensors may utilize a tunnel barrier layer toaugment the GMR internal structure and to provide increased sensitivity.

As shown in FIG. 1, write-head 106 may be longer along the x-axisdirection than read sensor 108. Accordingly, the active sensing portionof read sensor 108 is smaller than write-head 106, along the x-axis.Write-head 106 is used to magnetize nanoparticles 212A, 212B, and 212Cfor detection by read sensor 108 as discussed below. It is advantageousfor write-head to be longer in the x-direction than read sensor 108because it prevents read sensor from encountering unmagnetizednanoparticles, and thus, registering a false-negative detection of ananoparticle 212A, 212B, 212C.

Head-module 104 is kept in linear alignment with calibration trenches180 along the x-axis by position-error-servo (PES) read-head 192, whichreads magnetically encoded servo-alignment marks 193 from servo track194 on calibration assembly 100. PES read-head 192 may be, for example,an AMR, GMR, or TMR read sensor. In the example illustrated in FIG. 1,servo-alignment marks 193 shown are Timing Based Servo (TBS)servo-alignment marks such as those used in IBM® Linear Tape Open (LTO)tape drive products (e.g., IBM® tape product models TS1120 and TS1130).U.S. Pat. No. 6,320,719, entitled “Timing Based Servo System forMagnetic Tape Systems,” is hereby incorporated by reference in itsentirety for its showing of Timing Based Servo control and TBSservo-alignment marks. U.S. Pat. No. 6,282,051, entitled “Timing BasedServo System for Magnetic Tape Systems,” is hereby incorporated byreference in its entirety for showing the writing of TBS servo-alignmentmarks.

FIG. 5 illustrates an embodiment of a servo control system 500 forcontrolling the motion of head-module 104 in the x-axis and y-axis. Forsimplicity, FIG. 5 illustrates calibration assembly 100 including asingle trench 180. In addition, FIG. 5 shows a head module including asingle write-head 106 and read sensor 108 pair and a PES read head 192.However, it should be understood that the calibration assembly 100 mayinclude a plurality of trenches and the head module 104 may include aplurality of write-heads 106 and read sensors 108. PES read-head 192reads servo-alignment marks 193 in servo track 194. Processor 502receives position-error-servo (PES) signals from PES read-head 192.Processor 502 sends a signal to power amplifier 504 to control x-axisactuator 506 based on the PES information. In turn, the x-axis actuator506 controls the motion of head module 104 in the x-axis direction.X-axis actuator 506 is connected to head-module 104 via mechanicalconnector 508. Accordingly, head-module 104 can be positioned to centerwrite-head 106 and read sensor 108 on calibration trenches 180 ofcalibration assembly 100. Processor 502 also sends signals to poweramplifier 514 to control y-axis actuator 510 for conducting a scan byhead module 104 across calibration assembly 100. Y-axis actuator 510 isconnected to x-axis actuator via mechanical connector 512, such thathead-module 104 can be moved along the y-axis in a controllable manner.

FIG. 6 illustrates one embodiment of a write and read circuitry 600 foruse in writing to the calibration trenches 180 (i.e., magnetizingnanoparticles 212) and reading from the calibration trenches 180 (i.e.,sensing and detecting the magnetized nanoparticles 212). For simplicity,FIG. 6 illustrates calibration assembly 100 including a single trench180. In addition, FIG. 6 shows a head module including a singlewrite-head 106 and read sensor 108 pair. However, it should beunderstood that the calibration assembly 100 may include a plurality oftrenches and the head module 104 may include a plurality of write-heads106 and read sensors 108.

Processor 502 sends signals to power amplifier 604. Power amplifierprovides power to write-head 106 for magnetizing nanoparticles 212.Processor 502 also sends signals to power amplifier 616. Power amplifier616 powers Wheatstone bridge 606. In one embodiment, Wheatstone bridge606 includes read sensor 108 as one leg of the Wheatstone bridge and theremaining three legs of the Wheatstone bridge are resistors of the samenominal resistance as read sensor 108. One of these resistors inWheatstone bridge 606 may be adjustable so that the Wheatstone bridgemay be balanced to a null output when read sensor 108 is notexperiencing a magnetic field from a magnetized inner core 216 ofnanoparticles 212. Thus, read sensor 108 receives DC current from theWheatstone bridge 606. Read sensor 108 detects a resistance change basedon the magnetic field provided by the magnetized inner cores 216 ofnanoparticles 212. Wheatstone bridge 606 balances out the zero-magnetismresistance of read sensor 108 such that only the change in resistance ofread sensor 108 is sent to amplifier 614. The amplifier 614 receives thechange in resistance and sends the change in resistance to processor 502through filter 618. Filter 618 filters out noise. In one embodiment,filter 618 filters out 60 Hz noise, and any harmonics thereof, which isthe type of noise that is pervasive in an office or laboratory settingin which processes of the invention may be performed.

Processor 502 includes a matched filter 630, a table 620, and memory640. Processor 502 determines if a nanoparticle 212 was detected, andwhich nanoparticle 212 was detected utilizing the matched filter 630 andtable 620. The change in resistance of read sensor 108 is directlyproportional to the magnetic field provided by nanoparticle 212. Theidentification of the various nanoparticles simultaneously in the samesample assembly may be facilitated by the table 620 in processor 502.For example, a lookup table 620 contains a list of (a) nanoparticles and(b) the coercivity of the inner cores 216 of nanoparticles.

In one embodiment, the calibration assembly 100 may be used to calibratethe matched filter 630 of the write and read circuitry 600. Because thecalibration assembly 100 comprises nanoparticles 212 with known magneticproperties the read response of the read circuitry to a particularnanoparticle may be stored in the matched filter 630 as an ideal signalfor that nanoparticle. The ideal signal stored in the matched filter maythen be utilized for reliably and accurately detecting antigens.

For example, a correlation calculation is performed by the write andread circuit 600 of FIG. 6 to improve the detection accuracy of thenanoparticles 212. The processor 502 performs correlation calculationC(y) shown in Equation 1 between a detection signal profile g(y) read byread sensor 108 when a nanoparticle 212 is detected and a matched filter630.C(y)=∫g(η)h(η−y)dη  Equation 1In Equation 1, η is the integration variable along the y-axis thatvaries as read sensor 108 sweeps along the y-axis. The matched filter630 includes an impulse response h(y) of an ideal signal profile of adetected nanoparticle 212. Since h(y) is used repetitively, it may becalculated once and stored as matched filter 630 in processor 502. Forexample FIG. 7 illustrates the process of calculating an impulseresponse h(y) of an ideal signal profile of a detected nanoparticle.

Turning to FIG. 7, in step 702, the head module 104 with at least onemagneto-resistive read sensor 108 is swept along the y-axis of thecalibration assembly 100 at a known nanoparticle 212 location. Forexample, the head module 104 is swept along the y-axis of thecalibration assembly 100 at location y₁ shown in FIG. 3C where it isknown nanoparticle 212A is located. The magnetic properties ofnanoparticle 212A are known.

In one embodiment head-module 104 is moved linearly from left to rightalong the +y axis relative to a stationary calibration assembly. Inanother embodiment, the calibration assembly 100 is swept linearly fromright to left along the −y axis past a stationary head-module 104. Ifsubstrate 199 is of a flexible polyethylene terephthalate material, thenin one embodiment, this right-to-left motion may be performed as dataread-write operations in a magnetic tape drive. The head module 104 maysample a single calibration trench 180, or simultaneously sample aplurality of calibration trenches 180. As an alternate embodiment,head-module 104 comprises a helical-scan rotary head-module, and they-axis of the calibration trench 180 is at an angle to the substrate199. In this embodiment, the calibration trenches 180 are much shorterin length such that alignment of the head module 104 with calibrationtrenches 180 may be accomplished without alignment marks 193. In oneembodiment the IBM® MSS 3850 helical-scan tape drive may be utilized todetect nanoparticles 212.

In one embodiment the head module 104 comes into physical contact withthe upper surface 254 of the outer layer 253 during the sweeping step of702. Keeping the head module 104 in physical contact with the uppersurface ensures that the head module 104 is kept at a known z-axisposition and assists with alignment of head module 104 with calibrationtrenches 180. As discussed above, the outer layer 253 may comprisediamond-like-carbon, polytetrafluoroethylene, aluminum oxide,polyamides, or other low-friction materials known in the art.Accordingly, the low friction material of the outer layer assists thehead module 104 to smoothly sweep the calibration trenches 180 while inphysical contact with the upper surface 254 of outer layer 253, suchthat the nanoparticles of the calibration trench 180 are reliably andaccurately detected.

As discussed with respect to step 406 in FIG. 4, in some embodiments theinner core 216 of nanoparticles are demagnetized. Accordingly, in thisembodiment, as part of step 702, write-head 106 writes to nanoparticles212A, 212B, and 212C to magnetize inner cores 216A, 212B, and 212C ofnanoparticles. Write-head 106 writes with a constant DC magneticpolarity for the duration of the sweeping step 702, such that there areno unwritten regions of calibration assembly 100. In one embodiment,write-head 106 writes with magnetically-overlapping write pulses.Further in step 702, read sensor 108 detects the freshly magnetizedinner cores 216A, 216B, and 216C of nanoparticles 212A, 212B, and 212C.

Write head 106 magnetizes the inner cores 216 of nanoparticles 212 alongthe y-axis, which is the longitudinal-recording in the tape driveindustry. Read sensor 108 magnetically detects nanoparticles 212 alongthe y-axis. As a result, in step 702, the nanoparticles 212 may bemagnetized by write-head 106 and then immediately and magneticallydetected by read sensor 108 during a single sweep of the calibrationtrenches 180. As discussed above, this process is referred to as aread-after-write operation. In one embodiment the write-head 106 andread sensor 108 are separated by a magnetic shield (not shown) toprevent cross-talk between write-head 106 and read sensor 108 duringstep 702.

In another embodiment, the write-head 106 and the read sensor 108 arephysically separated sufficiently to avoid pick-up by the read sensors108 of the magnetic signals emanating from the write head 106 during theread-after-write operation. This embodiment can be accomplished bylocating the write-heads 106 in separate module(s) from the read sensors108 and aligning the read sensor 108 and write-head 106 pair(s) with aprecision alignment tool and bonding the modules together.

Alternatively, the steps of magnetizing nanoparticles 212 and the stepof detecting the nanoparticles 212 may be performed separately. Forexample, write head 106 magnetizes inner cores 216 of nanoparticles 212along the y-axis of calibration assembly 100. In one embodiment,write-head 106 is then turned off. Subsequently, read sensor 108magnetically detects nanoparticles 212 along the y-axis. The read modulesensor 108 may be swept across calibration trenches 180 along the y-axisin both the +y and −y directions. Accordingly, read sensor 108 canrepeatedly check for magnetized nanoparticles 212.

In an embodiment in which the number of calibration trenches 180 aregreater than the number of write-head 106 and read sensor 108 pairs inhead-module 104, the head-module 104 may scan the calibration trenches180 in a serpentine fashion. The head-module 104 performs a scan in the+y direction, as head-module 104 only provides read-after-writecapability in the +y direction as shown in FIG. 1. Then, a secondhead-module (not shown) comprising a mirror image of head-module 104,conducts a read-after-write operation in the −y direction.

In step 704, a read response is obtained for the nanoparticle 212. Readsensor 108 detects the magnetic properties of an inner core 216 based onthe materials used for that inner core 216. As discussed above, magneticinner cores 216 may comprise hard magnetic materials with highcoercivity, such as Fe₂O₃, CrO₂, and Barium Ferrite BaFe. For example,magnetic inner cores 216 may comprise iron oxide based nanoparticlematerials, including M Fe₂O₄ (where M may be Co, Ni, Cu, Zn, Cr, Ti, Ba,or Mg) nanomaterials, and iron oxide coated nanoparticle materials orother structures with similar functionality. As a result, in step 704,read sensor 108 may detect more than one type of nanoparticles 212 witha single sweep of the calibration assembly 100.

In step 706, the read response is stored. In one embodiment the readresponse is stored in the memory 640. In step 708 the processor 502 thenincrements the sample count. In step 710 the processor 502 determines ifthe sample count is less than a sample count threshold. The sample countthreshold is defined as the number of read response samples necessaryfor determining a correlation signal profile. The sample count thresholdmay be preconfigured by the manufacturer or defined by the user or otheradministrator.

If it is determined in step 710 that the number of sample counts is lessthan the sample count threshold, the process returns to step 702. Instep 702 the head module 104 with at least one magneto-resistive readsensor 108 is swept along the y-axis of the calibration assembly 100 atanother known nanoparticle 212 location (e.g. at nanoparticle 212Blocation shown at y₂ in FIG. 3C). If it is determined that the number ofsample counts is not less than the sample count threshold the processflows to step 712 in which the process determines the correlation signalprofile from the stored read responses. In step 714 the determinedcorrelation signal profile is stored. In one embodiment, the correlationsignal profile is stored in memory 640. In another embodiment thecorrelation signal profile is stored in the matched filter 630.

FIGS. 8A, 8B and 8C illustrate the use of the correlation equation(Equation 1 above) to create an analog correlation C(y) 803 from signal801 and matched filter 802 for the detection of a single nanoparticle212. FIG. 8A illustrates the detection signal profile g(y) read by readsensor 108 when a nanoparticle 212 is detected. The variable Arepresents the amplitude of the signal 801 from the read sensor 108 whena nanoparticle 212 is detected by the read sensor 108. As discussedabove, the magnetic read sensor 108 detects the magnetic properties ofan inner core 216 based on the materials used for that inner core 216.Accordingly, nanoparticles 212 with different inner cores 216 willresult in different detection signal profiles g(y).

FIG. 8B illustrates the impulse response h(y) of an ideal signal profile802 of the detected nanoparticle 212. The impulse response h(y) of anideal signal profile 802 may be stored in matched filter 630 for eachnanoparticle.

FIG. 8C illustrates the calculated correlation C(y) 803 for thedetection signal profile g(y) of each nanoparticle 212 detected by readsensor 108. The range of correlation C(y) is between −1 and +1, where +1represents an ideal correlation of one hundred percent (100%), 0indicates no correlation, and −1 indicates a completely reverse oropposite correlation.

In one embodiment, the manufacturer of the calibration assembly 100defines a manufacturer's correlation threshold 804. The manufacturer'scorrelation threshold 804 is a threshold correlation value that thecalibration assembly 100 must obtain during a calibration correlationtest (further discussed with respect to FIGS. 10A and 10B below) to bedeemed acceptable for calibration by the manufacturer. As discussedabove, the range of correlation C(y) is between −1 and +1, where +1represents an ideal correlation of one hundred percent (100%), 0indicates no correlation, and −1 indicates a completely reverse, oropposite correlation. In one embodiment, the manufacturer's correlationthreshold 804 is +0.8 such that the correlation is eighty percent (80%).However, it should be noted that the manufacturer's correlationthreshold may be any level of correlation that the manufacturer deems isacceptable for their customers. For example, the manufacturer'scorrelation threshold may be in the range of +0.6 to +0.98 such that thecorrelation is between sixty and ninety-eight percent.

Further, in one embodiment the user of the calibration assembly 100defines a user's correlation threshold 805. The user's correlationthreshold 805 is a threshold correlation value that the calibrationassembly 100 must obtain during a calibration correlation test (furtherdiscussed with respect to FIGS. 10A and 10B below) to be deemedacceptable by the user for calibration. In one embodiment, the user'scorrelation threshold 805 is +0.7 such that the correlation is seventypercent (70%). However, it should be noted that the user's correlationthreshold may be any level of correlation that the user deems isacceptable for their application. For example, the user's correlationthreshold in some embodiments may range between +0.4 and +0.95 such thatthe correlation is between forty and ninety-five percent. It should benoted that in most cases the manufacturer's correlation threshold ishigher than that of the user because the manufacturer must meet each andevery customer's user correlation thresholds.

As discussed above, the calibration trench 180 may have a plurality ofnanoparticles (e.g. nanoparticles 212A, 212B, and 212C etc).Accordingly, Equation 2 expresses the correlation C(j) for a finitenumber of discrete digital pulses.

$\begin{matrix}{{C(j)} = {\sum\limits_{i = 1}^{j}{{g(j)}{h\left( {j - i} \right)}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

FIGS. 9A, 9B and 9C illustrate the use of the digital correlationequation (Equation 2) to create a digital correlation C(j) 903 fromdiscrete digital pulses g(j) 901 and matched filter 902 for thedetection of a finite number of discrete digital pulses fromnanoparticles 212. For example, in one embodiment, in which there areeight (8) nanoparticles 212 positioned at known y-axis locations alongthe calibration trench 180 there are eight digital pulses. FIG. 9Aillustrates the detection signal g(j) read by read sensor 108 when eight(8) nanoparticles are detected as shown by eight (8) digital pulses ofsignal 901. The variable A represents the amplitude of the signal 901from the read sensor 108. Further, the variable M represents the numberof pulses detected by read sensor 108. FIG. 9B illustrates the impulseresponse h(j) of the ideal signal profiles 902 of eight (8) detectednanoparticles 212. The impulse responses h(j) of an ideal signal profile902 may be stored in matched filter 630. FIG. 9C illustrates thecalculated correlation C(j) 903 for the detected signal profiles g(j) ofthe eight (8) detected nanoparticles 212 by read sensor 108.

In one embodiment the manufacturer of the calibration assembly 100defines a manufacturer's correlation threshold 904. Again, themanufacturer's correlation threshold 904 is a threshold correlationvalue that the calibration assembly 100 must obtain during a calibrationcorrelation test (further discussed with respect to FIGS. 10A and 10Bbelow) to be deemed acceptable for calibration by the manufacturer. Inone embodiment, the manufacturer's correlation threshold 804 is +0.8such that the correlation is eighty percent (80%). However, it should benoted that the manufacturer's correlation threshold may be any level ofcorrelation that the manufacturer deems is acceptable for theircustomers. For example, the manufacturer's correlation threshold may bein the range of +0.6 to +0.98 such that the correlation is between sixtyand ninety-eight percent.

Further, in one embodiment the user of the calibration assembly 100defines a user's correlation threshold 905. As discussed above, theuser's correlation threshold 905 is a threshold correlation value thatthe calibration assembly 100 must obtain during a calibrationcorrelation test (further discussed with respect to FIGS. 10A and 10Bbelow) to be deemed acceptable by the user for calibration. In oneembodiment, the user's correlation threshold 805 is +0.7 such that thecorrelation is seventy percent (70%). However, it should be noted thatthe user's correlation threshold may be any level of correlation thatthe user deems is acceptable for their application. For example, theuser's correlation threshold in some embodiments may range between +0.4and +0.95 such that the correlation is between forty and ninety-fivepercent. Again, it should be noted that in most cases the manufacturer'scorrelation threshold is higher than that of the user because themanufacturer must meet each and every customer's user correlationthresholds.

In one embodiment, processor 502 compares this calculated correlationC(y) against a stored correlation signal profile Co before accepting thesignal g(y) as a valid detection of a nanoparticle 212.

In one embodiment, the ideal signal stored in the matched filter 630 ofthe write and read circuitry 600 is utilized in a manufacturer's anduser's correlation test of a calibration assembly 100 to ensure that thecalibration assembly is within the manufacturer's and user's acceptablestandards for calibration of their write and read assemblies. FIG. 10Aillustrates the process of performing a calibration correlation test fora calibration assembly 100. In one embodiment, the process begins withstep 1002 in which a manufacturer's correlation test is performed on thecalibration assembly. FIG. 10B provides further details of the steps ofperforming the manufacturer's correlation test on the calibrationassembly 100. For example, in step 1020 of FIG. 10B the head module 104with at least one magneto-resistive read sensor 108 is swept along they-axis of the calibration assembly 100 at a known nanoparticle 212location. For example, the head module 104 is swept along the y-axis ofthe calibration assembly 100 at location y₁ shown in FIG. 3C where it isknown nanoparticle 212A is located. The magnetic properties ofnanoparticle 212A are known. The process of sweeping head module overthe calibration assembly 100 is the same process as described withrespect to step 702 of FIG. 7 and is not repeated herein.

In step 1022 of FIG. 10B a read response is obtained for thenanoparticle 212A and the processor 502 determines a correlation of theread response. In an embodiment in which a single nanoparticle 212 isdetected, the processor 502 utilizes Equation 1 to determine acorrelation C(y) of the read response. In an embodiment in which aplurality of nanoparticles 212 are detected, the processor 502 utilizesEquation 2 to determine a correlation C(j) of the read response. Thecorrelation C(y) or C(j) during the manufacturer's correlation test isreferred to herein as the manufacturer's correlation.

Returning to step 1004 in FIG. 10A, the processor 502 determines if themanufacturer's correlation is greater than the manufacturer'scorrelation threshold 804 or 904. If the manufacturer's correlation isnot greater than the manufacturer's correlation threshold 804 or 904then the process proceeds to step 1006. In step 1006, if the correlationC(y) is at or below manufacturer's correlation threshold 804, or ifcorrelation C(j) is at or below manufacturer's correlation threshold904, then a manufacturer's correlation test error is indicated. In anembodiment in which a manufacturer's correlation test error is indicatedthe calibration assembly 100 may be rejected. A rejected calibrationassembly 100 should not be utilized for calibration by the manufactureror a user. In one embodiment, a rejected calibration assembly isdestroyed. Alternatively, in one embodiment, one or more read sensors108 of a head module 104 may be calibrated (as discussed further withrespect to FIG. 13) in response to the indication of a manufacturer'scorrelation test error.

However, if the manufacturer's correlation is greater than themanufacturer's correlation threshold 804 or 904, then the calibrationassembly 100 passed the manufacturer's correlation test. In step 1008the results of the manufacturer's correlation test are stored in thememory 640 of processor 502. Alternatively, or in addition, the resultsof the manufacturer's correlation test are stored in the matched filter630. A calibration assembly 100 that passes the manufacturer'scorrelation test indicates that the calibration assembly 100 is deemedacceptable by the manufacturer to be utilized for calibration by anyuser. Accordingly, the process proceeds to step 1010 in which thecalibration assembly 100 and the results of the manufacturer'scorrelation test are sent to a user.

In step 1012 the user performs a user correlation test on thecalibration assembly 1012. FIG. 10B provides further details of thesteps of performing the user's correlation test on the calibrationassembly 100. For example, in step 1020 of FIG. 10B the head module 104with at least one magneto-resistive read sensor 108 is swept along they-axis of the calibration assembly 100 at a known nanoparticle 212location. For example, the head module 104 is swept along the y-axis ofthe calibration assembly 100 at location y₁ shown in FIG. 3C where it isknown nanoparticle 212A is located. The magnetic properties ofnanoparticle 212A are known. The process of sweeping head module overthe calibration assembly 100 is the same process as described withrespect to step 702 of FIG. 7 and is not repeated herein.

In step 1022 of FIG. 10B a read response is obtained for thenanoparticle 212A and the processor 502 determines a correlation of theread response. In an embodiment in which a single nanoparticle 212 isdetected, the processor 502 utilizes Equation 1 to determine acorrelation C(y) of the read response. In an embodiment in which aplurality of nanoparticles 212 are detected, the processor 502 utilizesEquation 2 to determine a correlation C(j) of the read response. Thecorrelation C(y) or C(j) during the user's correlation test is referredto herein as the user's correlation.

Returning to step 1014 in FIG. 10A, the processor 502 determines if theuser's correlation is greater than the user's correlation threshold 805or 905. If the user's correlation is not greater than the user'scorrelation threshold 805 or 905 then the process proceeds to step 1016.In step 1016 if the correlation C(y) is at or below user's correlationthreshold 805, or if correlation C(j) is at or below user's correlationthreshold 905 then a user's correlation test error is indicated. In anembodiment in which a user's correlation test error is indicated thecalibration assembly 100 may be rejected. A rejected calibrationassembly 100 should not be utilized for calibration by the user. In oneembodiment, a rejected calibration assembly is destroyed. Alternatively,in one embodiment, the read sensor 108 may be calibrated (as discussedfurther with respect to FIG. 13) in response to the indication of auser's correlation test error.

However, if the user's correlation is greater than the user'scorrelation threshold 805 or 905, then the calibration assembly 100passed the user's correlation test. In step 1018 the results of theuser's correlation test are stored in the memory 640 of processor 502.Alternatively, or in addition, the results of the user's correlationtest are stored in the matched filter 630. A calibration assembly 100that passes the user's correlation test indicates that the calibrationassembly 100 is deemed acceptable by the user to be utilized forcalibration by that user.

Magnetic sensors, such as GMR sensors, contain magnetic materials whosecombined effect is to have a resistance change when subjected to amagnetic field. When subjected to low-level electrical overstress (EOS)or electrostatic discharge (ESD) current/voltage pulses the GMR sensorscan be damaged or degraded. Still further, corrosion or other agingprocesses can damage magnetic sensors over time, reducing the signalstrength and possibly leading to failure. In one embodiment, a method ofdetermine if a read sensor is damaged or degraded is described. Stillfurther, if it is determined that a read sensor is degraded, a method ofcalibrating a read sensor is described. Calibration of each individualread sensor allows for uniform read responses from each read sensor on aread head and prevents unreliable and inaccurate detection of analytesdue to degradation. If a read sensor 108 is degraded sufficiently bymild corrosion or ESD/EOS events, then it's ability to detect an analyteor to discriminate between the number of analytes may be jeopardized.Therefore, having a means to determine the response of the read sensor108 in situ is important for proper use of the read sensor 108.

The read sensor 108 described above may include a GMR stack. U.S. PatentApplication No. 2009/0268325, entitled “METHODS FOR DETECTING DAMAGE TOMAGNETORESISTIVE SENSORS,” is hereby incorporated by reference in itsentirety for its showing of magnetoresistive sensors.

FIG. 11 is a schematic diagram of a current-in-plane (CIP) read-sensorwhich may be used in conjunction with various embodiments, including theembodiment of read sensor 108. The sensor stripe 1106 is between a firstshield 1104 and a second shield 1102. The sensor stripe 1106 hasmultiple layers but is here depicted as a single sheet. Leads 1108extend from the sensor stripe 1106 so that an electrical connection canbe made. The sensor stripe 1106 has dimensions of width 1114, thickness1112, and height 1118. Also, the there typically is a gap 1116 betweenthe first shield 1104 and second shield 1102. The sensor stripe may havea hard bias magnet 1110 on either edge of the sensor stripe 1106 towardthe leads 1108. Below the first shield 1104 is the undercoat 1122, andabove the second shield 1102 is an overcoat 1120.

FIGS. 12A, 12B, and 12C can now be used to more fully understand thefollowing descriptions of several embodiments.

FIG. 12A shows a schematic diagram of the current flow through a genericGMR stack and the associated magnetic fields as viewed along a slice inthe stack when a forward (positive) bias current is applied. It shouldbe noted that a bias current is simply a current passed through thesensor, and no special characteristics or requirements should beattributed to the bias currents described herein unless otherwise noted.The vertical axes are in the stripe height orientation and thehorizontal axes are in the stripe thickness orientation. The track widthis into the page and the sample-bearing surface 1218 is at the top ofthe figure. The darkened circle represents current flow 1214 out of thepage. The magnetic field in the antiferromagnet (AFM) layer 1202 at theinterface with the adjacent ferromagnetic layer 1204 is represented byM_(AFM) on FIG. 12A and is assumed to be vertical. M_(AFM) could be thenet field in the AFM or the field at the interface of the first pinnedlayer (PL₁). M_(AFM) forces the magnetization (M_(P1)) in the firstpinned layer 1204 to also be in the vertical direction. The spacer layer1206 separates the second pinned ferromagnetic layer 1208 from thepinned layer 1204, and the proper thickness and coupling between thepinned layer 1204 and the second pinned ferromagnetic layer (PL₂) 1208results in the magnetization in the second pinned ferromagnetic layer1208 (M_(P2)) to be reverse-aligned with M_(P1). The layers describedcreate a synthetic antiferromagnet (SAFM). A copper layer 1210 separatesthe SAFM from the free layer (FL) 1212. The combination ofmagnetizations in the SAFM creates a magnetization (H_(PFL)) in the freelayer 1212, which is arbitrarily shown in the vertical orientation inFIG. 12A. The bias current flow (I_(mr)) in the stack generates amagnetic field in the AFM layer 1202 of H_(CAFM) and in the free layer1212 of H_(CFL). For forward bias current flow 1214, H_(CAFM) is alignedwith M_(AFM) and the magnetization of the first pinned layer 1204(H_(C)) is aligned with M_(P1), and aligned with M_(P2). H_(CFL) isreverse-aligned with H_(PFL).

FIG. 12B is a schematic diagram of the current flow through a genericGMR stack and the associated magnetic fields as viewed along a slice inthe stack when a reverse (negative) bias current is applied. It shouldbe noted that a bias current is simply a current passed through thesensor, and no special characteristics or requirements should beattributed to the bias currents described herein unless otherwise noted.All the definitions from FIG. 12A apply here, and instead of darkenedcircles, FIG. 12B has x's which indicate reverse bias current flow 1216,which is into the page. The combination of magnetizations in the SAFMcreates a magnetization (H_(PFL)) in the free layer 1212, which isarbitrarily shown in the vertical orientation in FIG. 12B. The biascurrent flow (I_(mr)) in the stack generates a magnetic field in the AFMlayer 1202 of H_(CAFM) and in the free layer 1212 of H_(CFL). Forreverse bias current flow 1216, H_(CAFM) is reverse-aligned withM_(AFM), H_(C) is reverse-aligned with M_(P1), and H_(CFL) is alignedwith H_(PFL).

FIG. 12C is a schematic diagram of the net magnetization (M_(FL)) insidethe free layer (1212 of FIG. 12A) for a forward biased sensor stripeformed by the vector sum of the magnetizations from the hard biasmagnets (M_(FLHB)) and the free layer magnetization H_(CFL). Also shownis the orientation of the magnetization M_(P2) is the second pinnedlayer (408 in FIG. 12A).

To first order, the change in resistance of the GMR sensor due to theGMR effect varies as the cosine of the angle between the magnetizationin the PL₂ and the FL. For the design described above, and shown inFIGS. 12A, 12B and 12C, due to the GMR effect, the reverse bias currentsresult in a slightly higher sensor resistance as compared with thesensor resistance for forward bias currents of the same magnitude. Oneof ordinary skill in the art would understand that if the designincluded a reverse of the magnetization of PL₂ (and thus of PL₁), theconverse would be true.

Returning to FIG. 11, the GMR read sensor includes leads 1108 and a hardbias magnet 1110 which are connected to the sensor stripe 1106. Thesensor stripes 1106 are made from stacks of metals deposited on a waferin a rectangular sheet (stripe) which has a width W, height H, and asheet resistance (R_(sheet)). The resistance is given by Equations 3Aand 3B:

$\begin{matrix}{R_{mro} = {R_{total} - R_{lead}}} & {{Equation}\mspace{14mu} 3A} \\{R_{mro} = {R_{sheet}\frac{W}{H}}} & {{Equation}\mspace{14mu} 3B}\end{matrix}$

Equation 3A gives the sensor stripe resistance (R_(mr)), which isdetermined by subtracting the lead-hard-bias resistance (R_(lead)) fromthe total measured resistance (R_(total)). Equation 3B gives the MRstripe resistance (R_(mro)) at ambient temperature and low bias currentin terms of R_(sheet) and the rectangular properties of the stripe. Thefabrication process includes polishing (lapping) a smoothhead-bearing-surface (HBS), which results in a given value of H for eachsensor, which usually has a wide tolerance range for manufactured parts.H, then can be determined from the measured value of R_(mro) using theknown values of W and R_(sheet) with Equation 3B.

Two main physical parameters which affect the GMR stripe resistance aremagnetic field and temperature, both of which are affected by thecurrent (I_(mr)) passing through the sensor stripe 1106. Externalmagnetic fields impinging on the sensor stripe 1106 will also affect thestripe resistance, as will be discussed below.

Since the current passing through the thin sensor also heats the sensorup due to Joule heating and the positive change in resistance withtemperature, the combined effects of heating and the GMR effect from themagnetic field generated by the bias current must be taken into account.As will be shown later, for a given current, the difference in theresistance measured with forward and reverse bias currents are, to firstorder, related to the GMR effect, while the sum of the two resistancesis dominated by the Joule heating effect.

The effect of temperature and magnetic field on the stripe resistance(R_(mr)) is given, to first order, by the following equations:R _(mr)(ΔT _(mr))=R _(mro)└[1+α_(mr) *ΔT _(mr)]−δ_(gmr)(ΔT_(mr))cos(θ)┘  Equation 4Aδ_(gmr)(ΔT _(mr))=δ_(gmro)[1−ΔT _(mr) /T _(C)]^(0.5)  Equation 4B

The first term in Equation 4A is the standard temperature dependence ofthe stripe resistance, with α_(mr) measured to be in the range of about0.001 to about 0.002° C.⁻¹ for extant GMR sensors, and R_(sheet) is onthe order of 10 to 25 Ω/sq. ΔT_(mr) is the temperature rise aboveambient temperature (e.g., about 25° C.). The second term in Equation 4Bis the GMR component to the resistance with δ_(gmr)(ΔT_(mr)) being thetemperature dependent fractional GMR resistance when the pinned layer(M_(PL)) and the free layer (M_(FL)) magnetizations are anti-parallel,and θ (from FIG. 12C) is the angle between M_(P2) and M_(FL) (θ=π/2+φ inFIG. 12C). Equation 4B gives a phenomenological formula for thetemperature dependence of δ_(gmr)(ΔT_(mr)). Extant GMR sensors have aδ_(gmro) nominally of around 5 to 15% at room temperature (ΔT_(mr)=0).In Equation 3D, T_(C) is a temperature, which experimentally isdetermined to be in the range of about 425° C. to 500° C. for a givensensor. H and W are the stripe height 1118 and the track width 1114 asindicated in FIG. 11.

In normal operation, M_(P2) and M_(FL) are designed to be almostperpendicular. The deviation from perpendicularity is due to therotation of M_(FL) by M_(P1) (φ_(PL)) and the magnetic field generatedby the bias current (H_(CFL)). It should be noted that a bias current issimply a current passed through the sensor, and no specialcharacteristics or requirements should be attributed to the biascurrents described herein unless otherwise noted. A current I_(mr) willgenerate a magnetic field H_(CFL) within the free layer, which to firstorder is given by Equation 5.

$\begin{matrix}{H_{CFL} = \frac{\mu_{0}{fl}_{mr}}{2H}} & {{Equation}\mspace{14mu} 5}\end{matrix}$where μ₀ is the permeability of free space, and H is the stripe heightof the read sensor 108, and f is a factor less than unity. The cosine ofthe angle θ, cos(θ), is then proportional to H_(CFL), and is given byEquation 6.cos(θ)≡εI _(mr).  Equation 6The stripe temperature rise versus bias current (I_(mr)) is assumed tobe proportional to the power in the stripe:

$\begin{matrix}{{\Delta\; T_{mr}} = \frac{{R_{mr}\left( {\Delta\; T_{mr}} \right)}I_{mr}^{2}}{\kappa_{mr}}} & {{Equation}\mspace{14mu} 7}\end{matrix}$κ_(mr), termed the thermal conductance, completely defines the sensorJoule heating. Combining Equation 3A through Equation 7 yields thefollowing.

$\begin{matrix}{{\Delta\; T_{mr}} = \frac{\left\lbrack {\gamma_{mr}/\alpha_{mr}} \right\rbrack{I_{mr}^{2}\left\lbrack {1 - {{ɛ\delta}_{gmr}I_{mr}}} \right\rbrack}}{1 - {\gamma_{mr}I_{mr}^{2}}}} & {{Equation}\mspace{14mu} 8A} \\{{{R_{mr}\left( I_{mr} \right)} = \frac{R_{mro}\left\lfloor {1 - {{ɛ\delta}_{gmr}I_{mr}}} \right\rfloor}{1 - {\gamma_{mr}I_{mr}^{2}}}}{{Where},}} & {{Equation}\mspace{14mu} 8B} \\{\gamma_{mr} = \frac{\alpha_{mr}{R_{mr}\left( {I_{mr} \geq 0} \right)}}{\kappa_{mr}}} & {{Equation}\mspace{14mu} 8C}\end{matrix}$

Since δ_(gmr) is a function of temperature, in Equations 8A and 8B,δ_(gmr) is a function of I_(mr). For small currents, δ_(gmr) can betreated as a constant. For higher currents, with large temperaturechanges, Equations 8A-8B must be solved numerically.

Accordingly, it can be shown that:

$\begin{matrix}{{R_{pnI}\left( I_{mr} \right)} = {\frac{{R_{mr}\left( I_{mr} \right)} - {R_{mr}\left( {- I_{mr}} \right)}}{2I_{mr}{R_{mr}\left( I_{mr} \right)}} \approx {ɛ\delta}_{gmr}}} & {{Equation}\mspace{14mu} 9A}\end{matrix}$A constant, K, can be defined as:K≡εδ_(gmr)  Equation 9Bwhere I_(mr) is the applied forward bias current and where −I_(mr) isthe reverse applied bias current, and is K is a calibration constant.Note that while c should be a constant for a given design and geometry,δ_(gmr), and thus K, will vary slightly for individual sensors. Factorswhich affect δ_(gmr) include, among others: stresses, process variationswithin a wafer, post-wafer processing variations, corrosion, and EOS/ESDdamage.

The purpose of a GMR sensor is to detect external magnetic fields.Knowing the strength of those fields yields important information. Theapplication of an external field of +H_(field) will result in a changein resistance given by:R _(mr)(H _(field))=R _(mr)(I _(mr))└1+βδ_(gmr) H _(field)┘  Equation 10

Measuring the GMR resistance at both +H_(field) and −H_(field) resultsin a GMR response (ΔR_(mr)) of:ΔR _(mr)(H _(field))=R _(mr)(H _(field))−R _(mr)(−H _(field))  Equation11AΔR _(mr)(H _(field))=2βδ_(gmr) H _(field) R _(mr)(I _(mr))=JH _(field) R_(mr)(I _(mr))  Equation 11BwhereJ=2βδ_(gmr)  Equation 11B

Both constants K and J are linearly proportional to δ_(gmr), where theproportionality are constants of the sensor geometry and other factors.If the sensors are damaged or age in the field, it is δ_(gmr) whichshould change, so the ratio of K/J should remain constant. Thus, initialvalues of both K (K_(o)) and J (J_(o)) may be determined for the readsensor 108 at the factory. J_(o) may be determined at the factory byread sensor 108 manufacturer by exposing the read sensor 108 to a knownexternal magnetic field. K_(o) may also be determined at the factorymeasuring the sensor resistance for at least one pair of bias currents(±I_(mr)) and using Equation 9A.

The read response of a read sensor 108 to an internal field H_(field)may be expressed as:

$\begin{matrix}{{{\Delta\;{R_{mr}\left( H_{field} \right)}} = {{JH}_{field}{R_{mr}\left( I_{mr} \right)}}}{with}} & {{Equation}\mspace{14mu} 12A} \\{J = {K\frac{J_{0}}{K_{0}}}} & {{Equation}\mspace{14mu} 12B}\end{matrix}$Solving for H_(field) gives:

$\begin{matrix}{H_{field} = {\frac{1}{K}{\frac{K_{0}}{J_{0}}\left\lbrack \frac{\Delta\;{R_{mr}\left( H_{field} \right)}}{R_{mr}\left( I_{mr} \right)} \right\rbrack}}} & {{Equation}\mspace{14mu} 12C}\end{matrix}$

As discussed above, the value of the calibration constant, K, can bemeasured by the user using Equations 9A and 9B above, and the initialvalues of the calibration constants K and J which are expressed as K_(o)and J_(o) respectively, may be determined by the manufacturer.Therefore, for a set bias current I_(mr), and with a read sensor 108having a measure resistance of R_(mr), and a change in resistance ofΔR_(mr) when the read sensor 108 is swept across a nanoparticle 212, thecalibrated magnetic field H_(field) may be calculated based on Equation12C.

Further, the manufacturer may define a range of acceptable values of theinitial calibration constant K₀ for a given read sensor 108. Forexample, the manufacturer may define a minimum acceptable value for theinitial calibration constant, K_(0min). In addition the manufacturer maydefine a maximum acceptable value for the initial calibration constant,K_(0max). In one embodiment, a manufacturer's defined acceptablecalibration constant range is defined, such that K_(0min)<K₀<K_(0max).If it is determined that the value of the initial calibration constantK₀ for a read sensor 108 is not within the manufacturer's definedacceptable calibration constant range the read sensor 108 is repaired orreplaced.

It is important to note that the value of the calibration constant K maychange with time. For example, the read sensor 108 may degrade over timedue to low-level electrical overstress (EOS) or electrostatic discharge(ESD) events. Therefore, the user may define a range of acceptablevalues of the calibration constant K for a given read sensor 108. Forexample, the user may define a minimum acceptable value for thecalibration constant, K_(umin). In addition the user may define amaximum acceptable value for the calibration constant, K_(umax). In oneembodiment, a user's defined acceptable calibration constant range isdefined, such that K_(umin)<K<K_(umax). If it is determined that thevalue of the calibration constant K for a read sensor 108 is not withinthe user's defined acceptable calibration constant range the read sensor108 is repaired or replaced. However, if it is determined that the valueof the calibration constant K for a read sensor 108 is within the user'sdefined acceptable calibration constant range then read sensor 108 iscalibrated. In one embodiment the user may define an acceptablecalibration constant range of 0.5<K/K_(o)<1.5.

FIG. 13 illustrates a process of calibrating a read sensor 108 of thehead module 108. In step 1302 the processor 502 measures the resistanceof the read sensor 108 upon an application of a forward bias current. Instep 1304 the processor 502 measures the resistance of the read sensor108 upon application of a reverse bias current. In one embodiment, theforward bias current and the reverse bias current have the samemagnitude. In step 1306 the processor 502 calculates the calibrationconstant for the read sensor 108. In one embodiment, the processor 502calculates the calibration constant K for the read sensor 108 utilizingEquation 9A as discussed above.

In another embodiment, the resistance of the read sensor 108 is measuredat several bias currents, including forward and reverse bias currents.Specifically, a plurality of first resistances are measured at aplurality forward bias currents and a plurality of second resistancesare measured at corresponding reverse bias currents. For exampleresistance values may be measured at 1, 2, 3, 4 and 5 mA. Herein, theplurality of resistances measured at forward bias currents arecollectively referred to as a plurality of first resistances. Similarly,a plurality of second resistances are measured at corresponding reversebias currents. For example, resistances may be measured at bias currentsof −1, −2, −3, −4 and −5 mA. Herein, the plurality of resistancesmeasured at reverse bias currents are collectively referred to as aplurality of second resistances. Accordingly, the calibration constant,K is determined based on the plurality of first measured resistances andthe plurality of the second measured resistances such that:

$\begin{matrix}{K = {\sum\frac{R_{pnl}\left( I_{mr} \right)}{N_{m}}}} & {{Equation}\mspace{14mu} 13}\end{matrix}$Where the Σ indicates the sum over the measured I_(mr), and N_(m) is thenumber of measurements. Accordingly, for I_(mr) of 1, 2, 3, 4 and 5 mA,N_(m) would be 5.

One of ordinary skill in the art would understand, that while an exampleof five first and second plurality of resistances are described, anynumber of plurality of first and second resistances could be measured attheir corresponding bias currents.

In step 1307, the processor determines if the calibration constant iswithin the user defined acceptable calibration constant range (i.e. isK_(umin)<K<K_(umax)) If it is determined that the calibration constant Kis not within the user defined acceptable calibration constant rangethen the process flows to step 1314. In step 1314 the read sensor 108 isdetermined unacceptable and the read sensor 108 is repaired or replaced.

However, if in step 1307 it is determined that the calibration constantK is within the user defined acceptable calibration constant range, suchthat K_(umin)<K<K_(umax), then the process flows to step 1308. In step1308 the calibration constant is stored. In one embodiment thecalibration constant is stored in the processor 502. Further, in oneembodiment, the calibration constant is stored in memory 640 of theprocessor 502.

In step 1310, a read response of the read sensor 108 to a nanoparticle.The read response may be obtained by sweeping a head module over acalibration assembly or any sample assembly having nanoparticlesobtained thereon. For example, the read response may be obtained asdescribed in FIG. 10B of the instant application by sweeping the readsensor 108 over a calibration assembly or by the step of sweeping theread sensor over sample assembly described with respect to FIG. 4 ofcopending and coassigned U.S. patent application Ser. No. 12/970,837entitled “TRENCHED SAMPLE ASSEMBLY FOR DETECTION OF ANALYTES WITHELECTROMAGNETIC READ-WRITE HEADS,” which is incorporated by reference.

In step 1312 the read response obtained in step 1310 is calibrated basedon the calibration constant K calculated in step 1306 utilizingEquations 12A, 12B and 12C. For example, for a set bias current I_(mr),and with the read sensor 108 having a measured resistance of R_(mr), anda change in resistance of ΔR_(mr) when the read sensor is swept across ananoparticle 212, the calibrated magnetic field H_(field) is becalculated based on Equation 12C.

Calibration of each individual read sensor in this manner allows foruniform read responses from each of the read sensors 108 on a read head104, and prevents unreliable an inaccurate detection of analytes due tosensor degradation or differences in sensor responses.

The terms “certain embodiments”, “an embodiment”, “embodiment”,“embodiments”, “the embodiment”, “the embodiments”, “one or moreembodiments”, “some embodiments”, and “one embodiment” mean one or more(but not all) embodiments unless expressly specified otherwise. Theterms “including”, “comprising”, “having” and variations thereof mean“including but not limited to”, unless expressly specified otherwise.The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise. Theterms “a”, “an” and “the” mean “one or more”, unless expressly specifiedotherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries. Additionally, a description of an embodiment withseveral components in communication with each other does not imply thatall such components are required. On the contrary a variety of optionalcomponents are described to illustrate the wide variety of possibleembodiments.

Further, although process steps, method steps, algorithms or the likemay be described in a sequential order, such processes, methods andalgorithms may be configured to work in alternate orders. In otherwords, any sequence or order of steps that may be described does notnecessarily indicate a requirement that the steps be performed in thatorder. The steps of processes described herein may be performed in anyorder practical. Further, some steps may be performed simultaneously, inparallel, or concurrently.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein changes and modification may be madewithout departing form this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims.

What is claimed is:
 1. A calibration assembly comprising: an outer layerhaving at least one calibration trench extending along a y-axis; and anencapsulation layer within said calibration trench, said encapsulationlayer having a plurality of nanoparticles spaced apart along said y-axisof said at least one calibration trench, wherein each of said pluralityof nanoparticles are provided at known y-axis locations within saidcalibration trench, and wherein each of said plurality of nanoparticleshave a known magnetic property.
 2. The calibration assembly of claim 1,further comprising magnetic servo alignment marks.
 3. The calibrationassembly of claim 2, wherein said calibration assembly further comprisesa servo alignment trench in said outer layer, said servo alignmenttrench parallel with said calibration trench.
 4. The calibrationassembly of claim 1, wherein said outer layer is selected from the groupconsisting of diamond-like-carbon, polytetrafluoroethylene aluminumoxide, and polyamides.
 5. The calibration assembly of claim 1, whereinsaid calibration assembly further comprises a base layer and whereinsaid base layer is selected from the group consisting of gold, silicon,and silicon oxide.
 6. A calibration assembly comprising: an outer layerhaving at least one calibration trench extending along a y-axis; and anencapsulation layer within said calibration trench, said encapsulationlayer having a plurality of nanoparticles spaced apart along said y-axisof said at least one calibration trench, wherein each of said pluralityof nanoparticles are encapsulated within said encapsulation layer,wherein each of said plurality of nanoparticles are provided at knowny-axis locations in said calibration trench, and wherein each of saidplurality of nanoparticles have a known magnetic property.
 7. Thecalibration assembly of claim 6, further comprising magnetic servoalignment marks.
 8. The calibration assembly of claim 7, wherein saidcalibration assembly further comprises a servo alignment trench in saidouter layer, said servo alignment trench parallel with said calibrationtrench.
 9. The calibration assembly of claim 6, wherein said outer layeris selected from the group consisting of diamond-like-carbon,polytetrafluoroethylene aluminum oxide, and polyamides.
 10. Thecalibration assembly of claim 6, wherein said calibration assemblyfurther comprises a base layer and wherein said base layer is selectedfrom the group consisting of gold, silicon, and silicon oxide.
 11. Acalibration assembly comprising: an outer layer having at least onecalibration trench extending along a y-axis; and an encapsulation layerwithin said calibration trench, said encapsulation layer having aplurality of nanoparticles spaced apart along said y-axis of said atleast one calibration trench, wherein said encapsulation layercomprising a cured polymer resin and each of said plurality ofnanoparticles being encapsulated within said cured polymer resin,wherein each of said plurality of nanoparticles are provided at knowny-axis locations in said calibration trench, and wherein each of saidplurality of nanoparticles have a known magnetic property.
 12. Thecalibration assembly of claim 11, further comprising magnetic servoalignment marks.
 13. The calibration assembly of claim 12, wherein saidcalibration assembly further comprises a servo alignment trench in saidouter layer, said servo alignment trench parallel with said calibrationtrench.
 14. The calibration assembly of claim 11, wherein said outerlayer is selected from the group consisting of diamond-like-carbon,polytetrafluoroethylene aluminum oxide, and polyamides.
 15. Thecalibration assembly of claim 11, wherein said calibration assemblyfurther comprises a base layer and wherein said base layer is selectedfrom the group consisting of gold, silicon, and silicon oxide.